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There is likely a "what do and what not to do" from the place that will be doing it that will give better insight than we do.

If it is 20 flight of stairs without a turn I would think you could put a slide under the leg that had been done, then use your remaining three to bug it up backwards without much issue.

You will want to do it in a way everything in that leg stays relaxed, you could practice ahead of time.